Semi-crystalline, semi-aromatic copolyamides

ABSTRACT

The present invention relates to semi-crystalline, semi-aromatic copolyamides, derived from terephthalic acid and mixtures comprising an alkylpentamethylenediamine and hexamethylenediamine.

The present invention relates to semi-crystalline, semi-aromaticcopolyamides derived from terephthalic acid and mixtures comprising analkylpentamethylenediamine and hexamethylenediamine, which have abending temperature under load (abbreviated BTUL; standards : NF T51005) under 1.8 MPa of at least 240° C., when these copolyamides arefilled with one or more padding or reinforcing fillers of fibrous typeand moulded. The present invention also relates to processes for theproduction of these copolyamides, as well as compositions, in particularfor moulding, produced from these copolyamides.

Polyamides derived from aliphatic diamine(s) and aliphatic or aromaticcarboxylic diacid(s) have already been known for a long time. Dependingon their composition, these polyamides are semi-crystalline polymershaving high melting points (m.p.) or completely amorphous substanceshaving relatively low glass transition temperatures (Tg).

Semi-crystalline polyamides are advantageously used when it is desiredto produce formed articles which have a good thermomechanical stabilityat high temperature. The best known of the semi-crystalline polyamidesis polyamide 6.6 (polymer of hexamethylenediamine and adipic acid); thispolyamide is easily convertible by the melt route, but, because of a lowTg of about 50° C., it finds fields of application which are restrictedto those involving use temperatures which remain below 100° C. Othersemi-crystalline polyamides have been disclosed which have a higher Tgand, consequently, a better retention of the mechanical property valuesas a function of temperature. A polyamide of this type which is ofparticular value is that obtained from terephthalic acid and2-methylpentamethylene-1,5-diamine (cf. JP-A-69/019.551) because of thepossibility of obtaining a Tg of the order of 142° C.; the stability toheat is clearly noted with a polyamide of this type, but it has beenfound that:

if this polymer is filled with a padding or reinforcing filler offibrous type and then converted by injection moulding under industriallyeconomic conditions using a cold mould, that is to say a mould kept at atemperature of between 100° and 150° C., with short cooling times (thetime concerned is the minimum time for which the injected material mustbe kept in the mould to enable the part to be ejected withoutdeformation or to enable the moulded product to fall from the mouldwithout difficulty), that is to say cooling times of between 20 and 40seconds,

it is not possible to obtain a high BTUL under 1.8 MPa able to reach andexceed 240° C. It has been found that this BTUL is, for example,145°-150° C. for moulded articles filled with 10 to 60% by weight ofglass fibres (relative to the weight of the total polyamide+filler) andobtained by the cold mould technique. The production, under thesemoulding conditions, of a low value for the BTUL is to be related to alow capacity for crystallisation of the polyamide under considerationobtained from terephthalic acid and alkylpentamethylenediamine, whichhas the result that when cooled rapidly, in particular when it isinjected into a cold mould, the said polyamide does not crystallise ordoes so only partially. The articles obtained may then be amorphous;moreover, they are liable to change as a result of a crystallisationduring reheating. It is understood that this type of semi-aromaticpolyamide is useable only when using a hot mould, that is to say a mouldkept at a temperature of between 170° and 200° C., with long coolingtimes, that is to say cooling times of between 2 and 4 minutes, andconsequently their development remains very limited.

European Patent No. 0,347,848 also discloses semi-crystalline polyamidesobtained from terephthalic acid, 2-methylpentamethylenediamine and anaromatic emine.

The use of a semi-crystalline, semi-aromatic polyamide based onrecurring units derived from terephthalic acid andalkylpentamethylenediamine, for moulding under industrially economicalconditions, therefore rests on the need to modify its capacity forcrystallisation. On leaving the cold mould, the polymer must haveacquired a semi-crystalline morphology throughout the mass of the part.

Continuing work in this field of the art, the Applicant has found:

that the rate of crystallisation may be increased to a level such thatit is possible to produce mouldings in a cold mould and to obtain, inparticular, moulded articles having, when they are filled with at leastone padding or reinforcing filler of fibrous type, a FTUL under 1.8 MPaof at least 240° C.,

by preparing copolyamides by using, alongside terephthalic acid, anamine reagent comprising an alkylpentamethylenediamine andhexamethylenediamine.

More specifically, the present invention relates to thesemi-crystalline, semi-aromatic copolyamides obtained from-reagentscomprising terephthalic acid (or a derivative) and2-methylpentamethylenediamine, these copolyamides being characterised bythe following points:

they contain in their structure recurring units of formula (I), (II),(III) and (IV), ##STR1## the units of formula (III) being optional,

the molecular ratio of units (I) with respect to the sum of units(II)+(III)+(IV) is 1;

the amount of units (III) in the mixture (II)+(III) is in the rangeranging from 0 to 5 mol % and that of the units (II), with respect tothe same reference, is in the range ranging from 100 to 95 mol %;

the amount of units (IV) in the mixture (II)+(III)

+(IV) is in the range ranging from 40 to 90 mol %; and

they also contain a proportion of non-conforming units derived frombis-hexamethylenetriamine, expressed as a percentage by weight ofbis-hexamethylenetriamine with respect to the weight of the copolyamideobtained, which is less than 0.5% and more precisely is within the rangeranging from 0.01 to 0.5%.

If the amount of units (IV) becomes greater than 90 mol %, the meltingpoint (m.p.) of the copolyamides obtained increases to a level such thatthe difference between the m.p. and the decomposition temperature of thecopolyamide becomes too small, that is to say a difference having valuesof less than 30° C., and the copolyamide is degraded during itsconversion by injection moulding and the thermomechanical properties ofthe moulded articles obtained are reduced.

If the amount of units (IV) becomes less than 40 mol %, it has beenfound that the capacity of the copolyamides for crystallisation isinsufficient and that it is not possible to obtain the desired BTULvalues. More precisely, the thermal melting-crystallisation propertiesare determined by differential calorimetric analysis (DSC) using aMETTLER type TA 3000 DSC 30 apparatus, operating under nitrogen andusing a well-defined heat cycle, which will be defined below. Thefollowing values are used from the results obtained: m.p.=temperature atthe top of the melting peak; Tcr=temperature at the top of thecrystallisation peak during cooling; ΔT=m.p.-Tcr. The temperaturedifference ΔT is lower the greater the capacity of the copolyamide forcrystallisation. If the amount of units (IV) becomes less than 40 mol %,it has been found that the temperature difference ΔT assumes valueswhich correspond to an inadequate capacity for crystallisation, whichare higher than 60° C.

According to a preferential modality, the copolyamides of the presentinvention have a structure as defined above, in which the amount ofunits (IV) in the mixture (II)+(III)+(IV) is within the range rangingfrom 45 to 75 mol %; under these conditions the temperature differenceΔT, which is low, assumes values which are within the range ranging from10° to 55° C.

With regard to their molecular values, the copolyamides according to thepresent invention (taken in its general preferential subject) have:

viscosity characteristics, expressed as the viscosity index (IV)measured in accordance with the standard ISO R 307 (2nd Edition, 1984)on a solution containing 0.5 g of polymer (dried for 2 hours at 60° C.while sweeping with argon) in 100 cm³ of metacresol or of 95% by weightconcentrated H₂ SO₄, which are at least 60 ml/g and way be between 80and 250 ml/g; and

number-average molecular masses (Mn), determined by determining the endgroups and the non-conforming units, which are at least 9,000 g/mol andmay be between 10,000 and 25,000 g/mol.

With regard to their thermomechanical values, the copolyamides accordingto the present invention (taken in its general or preferential subject)have, in particular:

Tgs, measured by DSC analysis, which are at least 120° C. and may bebetween 125° and 140° C.; and

BTULs under 1.8 MPa, determined in accordance with the standard NF T51005, which are at least 240° C. and may be between 250° and 310° C.,when the copolyamides are filled with, for example, 10 to 60% by weight(with respect to the weight of copolyamide+filler) of at least onepadding or reinforcing filler of fibrous nature.

The units of formula (I) originate from terephthalic acid or aderivative, such as, for example, a dihalide or a diester.

The units of formula (II) are obtained from2-methylpentamethylene-1,5-diamine. With regard to the optional units offormula (III), these are derived from 2-ethyltetramethylene-1,4-diamine.The synthesis of the 2-methylpentamethylenediamine used may be carriedout by hydrogenation of 2-methylglutaric acid dinitrile in accordancewith known processes. Similarly, the synthesis of2-ethyltetramethylenediamine may be carried out by hydrogenation of2-ethylsuccinic acid dinitrile.

With regard to the units of formula (IV), these originate fromhexamethylene-1,6-diamine.

With regard to the non-conforming units, their structure is derived frombis-hexamethylenetriamine H₂ N - ( CH₂)₆ --N--(CH₂)₆ --NH₂. Thesenon-conforming units of structure (v) represented by: --HN --(CH₂)₆--NH--(CH₂)₆ --NH-- and/or --HN--(CH₂)₆ --N--( CH₂)₆ --NH--are formedduring the polycondensation reaction by a dimerisation reaction of thehexamethylenediamine starting material and/or its derivative involved inthe polycondensation reaction and having a single free NH₂ group. Thepresence of the non-conforming units in amounts greater than 0.5% byweight has the effect, in particular, of causing an undesirable increasein the viscosity characteristics, in the finished copolyamide.

The copolyamides according to the present invention may be prepared byapplication of polycondensation processes well known to experts in thepolymer field: polycondensation by a thermal route, carrying out thereaction in the molten mass or in the presence of an organic solvent orsolvents, from the diacid (terephthalic acid; or acid reagent) anddiamines (methylpentamethylenediamine+hexamethylenediamine+, optionally,ethyltetramethylenediamine; or amine reagent); polycondensation insolution or interfacial polycondensation using a dihalide of the diacidand diamines as starting materials.

In order to carry out this polycondensation, and this constitutesfurther subjects of the present invention, it is preferred-to employ thethermal route.

A first convenient process of this type, which applies verypreferentially when the composition of the starting reagents comprises40 to 60 mol % of hexamethylenediamine in the mixture of diamines,comprises the technique of polycondensation in the molten mass,according to which a starting composition: * containing: (i) eitherstoichiometric amounts, or close to stoichiometric amounts, of diacidand diamines supplying equal or virtually equal numbers of COOH and NH₂groups, or their stoichiometric salt(s) with, optionally, an excess ofdiacid and/or of diamine(s) in the free state, (2i) water in an amountsufficient to allow the distillation in step 1 indicated below to becarried out under the specific temperature (T1 and T2) and pressure (P)conditions also indicated below, and (3i), optionally, a catalyst, * ispolycondensed by carrying out the reaction in a closed system of theautoclave type, and * by linking the following steps:

Step 1: in which, the autoclave being closed, the temperature of thestarting composition is progressively increased up to a specific valueT1 which is within the range ranging from 170° C. to 240° C.; then,under a constant pressure P equal to the autogenous water vapourpressure obtained, which is within the range ranging from 0.7 to 2.6MPa, the water present in the reaction mass is removed by regulardistillation, whilst progressively raising the temperature of thecomposition at the same time to a value T2 which is higher than thetemperature T1 reached before distillation and is within the rangeranging from 215° C. to 320° C.;

Step 2: in which the pressure is progressively lowered from theautogenous pressure value to atmospheric pressure value and, optionally,at the same time, the temperature of the composition is raised to avalue T3 which is higher by ten to several tens of degrees Celsius thanthe temperature T2 reached before decompression, whilst continuing toensure regular distillation of water throughout this decompressionperiod;

Step 3: in which the polycondensation reaction is completed by stirringthe reaction composition for a certain time, carrying out the reactionunder atmospheric pressure and optionally/or under a lower pressure witha mass temperature equal to or higher than the temperature T2 or T3obtained at the end of Step 2, for a sufficient period enabling apolyamide having the desired molecular and viscosity characteristics tobe obtained.

The expression "water present in the reaction composition", which isused above in Step 1 with reference to the distillation, is understoodto define the water contained in the starting compositions plus thewater which may form as a result of the polycondensation reaction of theacid reagent and the amine reagent. The amount of water contained in thestarting compositions is not critical from the point where it enablesthe distillation in Step 1 to be conducted under the particulartemperature (T1 and T2) and autogenous pressure (P) conditions indicatedabove; this amount of water may be determined easily by a person skilledin the art on the basis of his ordinary knowledge and with the aid ofsimple tests.

In order to carry out Step 1 of the polycondensation process which hasJust been described, it is possible to use starting compositions whichare in the form of mixtures: either based on the acid reagent, the aminereagent, water and, optionally, catalysts, the acid reagent being usedin the solid form and the amine reagent being used, for example, in theform in which it naturally occurs or in the form of an aqueous solution;or based on the diacid salt or salts and diamine, water and, optionally,diacid and/or diamine(s) in the free state and catalysts, the salt orsalts being used, for example, in the solid form, in aqueous dispersionor in the form of an aqueous solution.

With regard to the catalyst (3i) which may be used, this generallyconsists either of a compound (Δ) or of a compound (β), (α) denoting aninorganic oxygen-containing monoacid or polyacid or an organicoxygen-containing monoacid or polyacid other than a carboxylic acid, atleast one of the acid groups of which has an ionisation constant pka inwater at 25° C. equal to or less than 4 and (β) denoting an alkali metalor alkaline earth salt of said acid.

The strong acids (α) used are preferably the acids derived fromphosphorus and more particularly hypophosphorous, phosphorous,orthophosphoric, pyrophosphoric, methylphosphonic, phenylphosphonic,benzylphosphonic, dimethylphosphinic, diphenylphosphinic,methylphenylphosphinic, dibenzylphosphinic, methylphosphonous,phenylphosphonous or benzylphosphonous acids.

With regard to the acid salt (β), use is generally made of alkali metalsor alkaline earth metal salts derived from inorganic or organic oxyacids(α).

Salts (β) preferably used are those which are completely soluble in thereaction mixture. Amongst these preferred salts (β), the suitable saltsare the sodium and potassium salts obtained from the particular types ofinorganic or organic oxyacids (α) which are suitable and have beenmentioned above. The salts (β) which are very particularly suitable arethe sodium and potassium salts obtained from the preferred acids derivedfrom phosphorus which have been mentioned by name above.

The proportions of strong acid (α) or salt (β), expressed as apercentage by weight with respect to the final copolyamide, aregenerally between 0.01 and 1% and preferably between 0.01 and 0.5%.

With regard to the way in which Step 1 of the polycondensation processunder discussion is conducted, it should be noted that the progressiveheating of the starting composition up to the temperature T1 may becarried out over a period ranging, for example, from 10 minutes to 2hours. With regard to the distillation under constant autogenouspressure P, this is carried out over a period of time ranging, forexample, from 30 minutes to 3 hours 30 minutes.

When carrying out Step 1, it will be preferred (and this preferencerelates only to Step 1 of the first convenient process) to carry out thedistillation under a constant autogenous pressure P which is within therange ranging from 0.9 to 1.8 MPa, choosing: a temperature T1 at thestart of distillation which is within the range ranging from 190° C. to215° C. and a temperature T2 Just before decompression which is withinthe range ranging from 235° C. to 310° C. and still more preferentiallyranging from 265° C. to 300° C.

When carrying out Step 2, the decompression, which may proceed insuccessive stages, is carried out over a period ranging, for example,from 20 minutes to 2 hours 30 minutes and, preferably, the temperatureof the reaction mass is raised at the same time to a value T3 which is,for example, within the range ranging from 300° C. to 340° C.

When carrying out Step 3, the polycondensation reaction is terminated byallowing the reaction mass to react at the temperature T3 or at atemperature which may be higher, by a few degrees to about ten degrees,than T3, preferably working under a reduced pressure which is within therange ranging from 1.10² to 1000.10² Pa for a period of time (includingthe time for applying reduced pressure) ranging, for example, from 10minutes to 3 hours.

A second convenient process for mass polycondensation, which alsoapplies satisfactorily whatever the proportions of hexamethylenediaminein the mixture of diamines, consists in subjecting the startingcomposition, which has been defined above, to a polycondensationreaction using Step 1 of the first convenient process, which has Justbeen defined, and then linking the following steps:

Step 2': in which the reactor is emptied rapidly, over a period rangingfrom 5 minutes to 30 minutes: during this period, the autogenous watervapour pressure is lowered from the autogenous pressure value toatmospheric pressure value and, working under an inert atmosphere(nitrogen), the prepolymer formed is recovered and then cooled andconverted to a powder by grinding;

Step 3': in which the reaction for completion of the polycondensation iscarried out by conducting the post-condensation of the prepolymer inpowder form obtained either in the solid phase, working in a reactorkept under a pressure, optionally in the presence of inert gas(nitrogen), of between the atmospheric pressure value and a lower valueof 0.1.10² Pa, at a temperature ranging from 200° C. to 280° C. and fora sufficient period enabling a copolyamide to be obtained, having thedesired molecular and viscosity characteristics, ranging, for example,from 10 minutes to 5 hours; or in the molten phase, working in anextruder-degasser containing one or more screws, the essential operatingparameters of the said extruder-degasset comprising: the temperature ofthe reaction zone, which is within the range ranging from 310° C. to360° C., the devolatilisation pressure for this zone, which is withinthe range ranging from the atmospheric pressure value to a lower valueof 0.1.10² Pa, and the residence time of the prepolymer in theextruder-degasset, which is within the range ranging from 30 seconds to5 minutes; or by linking post-condensation in the molten phase andpost-condensation in the solid phase.

A third convenient process, which again also applies whatever theproportions of hexamethylenediamine in the mixture of diamines,comprises the thermal polycondensation technique conducted in solution,according to which the following steps are linked:

Step 1'': conducted under an inert atmosphere (nitrogen), in which stepthe starting composition, containing the elements (i) and (3i), whichhave been referred to above with regard to the starting mixture for thefirst and second processes, is dissolved in an aprotic polar solvent ora mixture of such solvents having a boiling point higher than 220° C.,working at ambient temperature of 20° C. to 30° C., the temperature ofthe solution obtained is then raised to the desired reaction temperatureof between 190° C. and 220° C. and the water of amidification is removedby regular distillation under atmospheric pressure for a period rangingfrom 20 minutes to 2 hours;

Step 2'': again conducted under an inert atmosphere, in which step thetemperature of the reaction solution is raised to a value above theboiling point of the solvent or solvents used and the remainder of thewater of amidification and the solvent or solvents present are thenremoved, again by distillation under atmospheric pressure;

Step 3'': in which, once the solvent or solvents have been removed, thepolycondensation is completed by allowing the reaction mass to react ata temperature ranging from 300° to 340° C., operating under a reducedpressure which is within the range ranging from 0.1.10² Pa to 1.10² Pafor a sufficient period (including the period for applying reducedpressure) enabling a copolyamide to be obtained having the desiredmolecular and viscosity characteristics, ranging, for example, from 10minutes to 1 hour.

Suitable solvents are, in particular, 1,3-dimethyl-2-imidazolidone,1,3-dimethyl-3,4,5,6-tetrahydro-2-pyrimidone, tetramethylsulphone,diphenyl sulphoxide and a mixture of these solvents.

The processes which have Just been described may be applied tocompositions comprising either stoichiometric amounts of an acid reagentand an amide reagent supplying equal numbers of COOH and NH₂ groups, ortheir stoichiometric salt(s).

It may be advantageous to use amounts of amine reagent which are higherthan those Just necessary to obtain equivalents between the COOH and NH₂groups in the starting compositions, so as to introduce into thereaction mass an excess of diamine(s), making it possible to compensatefor the loss of this reagent, which is essentially involved during thedistillation operation under constant pressure (Step(s) 1 or 1''+2'')and then during the decompression operation (Step 2 or 2'). Within theframework of this advantageous method, the excess amine reagent,expressed by the molar percentage of amine reagent in excess inaccordance with the relationship: ##EQU1## is usually within the rangeranging from 0.5 to 6% and preferably ranging from 1 to 4%.

The processes which have just been described offer a possibility forpreparing semi-crystalline, semi-aromatic copolyamides from an aminereagent comprising an alkylpentamethylenediamine andhexamethylenediamine, reducing the development of parasitic reactions(which will be mentioned further below) which involve these diamines andgive rise, in particular, to a loss in total basicity.

2-Methylpentamethylene-1,5-diamine is a compound which cyclises easily;this cyclisation, when it relates to the free diamine, gives rise to3-methylpiperidine (which product is termed "free cyclic amine" below)with liberation of ammonia NH₃, and when it relates to the diamineinvolved in the amidification reactions by only one of its functionalgroups, it acts as a chain-limiting mechanism giving rise to blockinggroups of formula: ##STR2## also with liberation of ammonia. The freecyclic amine formed is recovered essentially at the time at which thewater is removed by distillation under constant pressure (Step(s) 1 or1''+2'') and then during decompression (Step 2 or 2'). Another parasiticreaction consists in the loss of amine reagent (in particular2-methylpentamethylenediamine and hexamethylenediamine) by entrainment,which occurs essentially at the time when the water present is. removedby distillation under constant pressure (Step(s) 1 or 1''+2'') and thenduring decompression (Step 2 or 2'). The result of these parasiticreactions therefore manifests itself in two adverse effects:

on the one hand, a loss of total basicity involving, on the one hand, aloss of stoichiometry during the polycondensation reaction between theprimary amino groups and the carboxyl groups which are reacting,consequently precluding the possibility of easily increasing themolecular mass of the polyamide being formed, and, on the other hand, areal difficulty for industrial reproduction of the process employed. Theloss in total basicity which has been mentioned above is establishedwith respect to the total amount of amine reagent employed and isexpressed by the equation: ##EQU2##

the expression "basicity lost" corresponds to the sum: number of NH₂equivalents of the amine reagent lost during distillation+number of NHequivalents of free cyclic amine+number of NH₂ equivalents of ammonia.This lost basicity is determined directly, by means of a potentiometricdetermination, on the distillates, that is to say all of the watercondensed during the distillation stages under constant pressure andduring decompression;

the expression "basicity used" corresponds to the number of NH₂equivalents of the amine reagent used. The expression "number ofequivalents" of primary or secondary amino of a compound defines thenumber of primary or secondary amino groups contained in one mol of thesaid compound; for example one mol of amine reagent comprising2-methylpentamethylenediamine contains 2 primary amino equivalents NH₂whereas one mol of cyclic amine comprising 3-methylpiperidine containsone secondary amino equivalent NH:

and, on the other hand, the existence in the polycondensation mixture ofa high proportion of terminal groups of the cyclic amine type, whichhave the role of limiting the chain and may limit access to highmolecular masses.

Using the process which have Just been described for the preparation ofsemi-aromatic copolyamides, a limited loss of total basicity isobtained, which may be at values of less than 6% and may reach values aslow as those between 1 and 4%. Also, copolyamides are obtained whichhave a limiting proportion of terminal groups of the cyclic amine type,which act as chain limiter, which proportion may be at values of lessthan 70 milliequivalents per kilogram of polymer (meq/kg) and may reachvalues as low as those between 2 and 50 meq/kg; the determination ofthese proportions of terminal groups of the cyclic amine type is carriedout in accordance with the indications given below.

One or more additive(s) customarily used during the preparation ofpolyamides may be added to the copolyamides of the invention, before,during or towards the end of the polycondensation reaction. Theseadditives are, for example, antioxidants, flame retardants, lightstabilisers, heat stabilisers, mould-release agents, opticalbrighteners, colorants and the like.

It is also possible to use padding or reinforcing fillers, which may beadded to the copolyamides using techniques which make use of the mixtureof powders and/or granules, or, alternatively, may be incorporatedtherein in the molten Jet, by remelting the copolyamides in suitableequipment, such as, for example, an extruder. The fillers which may beadded are very diverse. They may be a fibrous material such as: asbestosfibres, carbon fibres, metal carbide or nitride or metalloid carbide ornitride fibres, such as silicon carbide, silicon nitride or boroncarbide fibres; glass fibres; organic fibres able to withstand heat; andmixtures of two or more than two of the abovementioned fibrousmaterials. The filler may also consist, in particular, of: glassmicrospheres; mica flakes; talc; or combinations of two or more than twoof the abovementioned non-fibrous materials; or combinations of at leastone fibrous material with at least one of the abovementioned non-fibrousmaterials. Amongst these fillers, glass fibres are particularlypreferred. These glass fibres may be ordinary glass fibres or treatedglass fibres, for example glass fibres treated with the aid of silane.In general, these glass fibres have a diameter of between 3 and 30 μmand a length of less than 10 mm.

The compositions thus obtained (and these comprise another subject ofthe present invention), containing a copolyamide and at least onefiller, may easily be converted, for example by injection moulding;these compositions may contain one (or more) filler(s) in an amountwhich may reach 80% of the weight of the polymer+filler(s) system. Theproportion of filler(s) is preferably between 10% and 60% and still morepreferentially between 30% and 60%.

The copolyamides according to the invention may be converted usingconventional machines, for example injection, extrusion or spinningmachines, to give shaped objects such as, in particular, massive mouldedarticles, filaments or fills. With regard to the conversion conditions,the copolyamides according to the invention, optionally containingfillers, may, for example, be injected easily using a materialtemperature which is not too high, such as those ranging, for example,from 310° to 350° C.

The examples which follow show, in a non-limiting manner, how thepresent invention may be implemented.

In these examples, some checks are carried out. The methods by whichthey are carried out are indicated below:

DETERMINATION OF THE PROPORTION OF TERMINAL COOH GROUPS (COOH TG) andNH₂ GROUPS (NH₂ TG) IN THE POLYMER:

This determination is carried out by potentiometric determination of apolymer solution using 0.02N trifluoromethanesulphonic acid. The methodpermits the simultaneous determination of COOH and NH₂ groups by theaddition of a 0.05N solution of tetrabutylanunonium hydroxide innitrobenzene. The results are expressed in milliequivalents per kilogramof polymer (meq/kg).

DETERMINATION OF METHYLPIPERIDINE IN THE POLYMER:

The determination of 3-methylpiperidine (MPP) in the polymer is carriedout by gas phase chromatography. The principle of the method is asfollows:

the polymer first undergoes hydrolysis in hydrochloric acid and is thenneutralised with sodium hydroxide solution to a slightly basic pH,

the amines are then extracted quantitatively with chloroform, and

this chloroform extract is finally analysed by gas phase chromatographyand the 3-methylpiperidine is determined by the internal standardmethods. The number of terminal MPP groups (MPP TG) in the polymer is inthis case also expressed in meq/kg.

DETERMINATION OF BIS-HEXAMETHYLENETRIAMINE (BHT) IN THE POLYMER:

This determination is carried out by gas phase chromatography. Theprinciple of the method is as follows:

the polymer first undergoes hydrolysis in hydrochloric acid and is thenneutralised with sodium hydroxide solution to a slightly basic pH,

the amines are then extracted quantitatively with chloroform and thechloroform extract obtained is concentrated by evaporation ofchloroform, and then

the concentrated solution obtained is finally analysed by gas phasechromatography and the BHT is determined by the internal standardmethod. The BHT content will be given in millimoles per kilogram ofpolymer (mM/kg) and in % by weight in the polymer (1 mM of BHT=0,215 g).

DETERMINATION OF THE VISCOSITY INDEX (IV) FOR THE POLYMER:

This index is determined at 25° C. in accordance with internationalstandard ISO 307, 2nd Edition, 1984, on a solution containing 0.5 g ofpolymer (dried for 2 hours at 60° C. while sweeping with argon) in 100cm³ of metacresol. For polymers rich in hexamethylenediamine, in thecase where the polymer may not be dissolved in metacresol, aconcentrated 95% by weight H₂ SO₄ is then used.

DETERMINATION OF THE LOST BASICITY IN THE DISTILLATES:

The basicity is determined by simple potentiometric determination by HClon all of the water condensed during the distillation stages underconstant pressure and during decompression.

DETERMINATION OF THE THERMAL CHARACTERISTICS OF THE POLYMER:

This determination of the thermal characteristics is carried out bydifferential calorimetric analysis (DSC) using a Mettler type TA 3000DSC 30 apparatus. The determination is carried out under nitrogen inthree steps (heat cycle):

rise from 25° C. to 350° C. at a rate of 10° C./min; holding for 2minutes at 350° C.; this step serves to obliterate the thermal historyof the polymer;

lowering from 350° C. to 25° C. at a rate of 10° C./min; this stepserves to obtain the crystallisation temperature on cooling (Tcr);

reheating from 25° C. to 350° C. at a rate of 10° C./min; this stepserves to obtain the glass transition temperature (Tg) and the meltingpoint (m.p.) of the polymer.

EXAMPLE 1

In this example the preparation of a semicrystalline copolyamide fromterephthalic acid, 2-methylpentamethylenediamine andhexamethylenediamine (50 mol % in the mixture of diamines) by the moltenmass process termed the "first convenient process" is described.

1) Preparation of the diamines (2-methylpentamethylenediamine andhexamethylenediamine)/terephthalic acid salt in aqueous solution:

The reaction is carried out in a 10 liter glass reactor equipped with:

a heating system,

an anchor-type stirrer,

a system allowing sweeping with nitrogen and maintenance of anoxygen-free atmosphere, and

a system enabling condensation of the volatile products.

The following are introduced cold into the reactor, which is kept sweptunder a gentle stream of nitrogen:

1079.7 g of terephthalic acid (6.504 mols),

793.6 g of 2-methylpentamethylenediamine (6.841 tools),

1834.1 g of dry crystalline hexamethylenediamine/terephthalic acid salt(6,509 mols),

3.8 g of hexamethylenediamine (0.033 mol), and

3707 g of distilled water.

The temperature of the composition is raised to 75° C. and the mixtureis stirred for 2 hours, maintaining sweeping with nitrogen. The pH of a10% by weight aqueous salt solution is then determined at 20° C. A pH of9.18 is obtained; in this example a 5.18% molar excess of2-methylpentamethylenediamine and a 2.84% molar excess of amine reagentare used.

2) Polycondensation in an autoclave:

The apparatus used consists of a 7.5 liter stainless steel stirredautoclave equipped to operate at up to 340° C. and a pressure of 2.2MPa. It is provided with:

a double-walled heating system operating by a heat transfer fluid,

a frame-type stirrer,

a system enabling the autoclave to be placed under nitrogen pressure,

a circuit enabling the volatile products to be condensed and collected,

and a device for establishing a pressure lower than atmosphericpressure.

7,361 kg of the aqueous salt solution prepared above are introduced with3.2 g of a 50% by weight aqueous hypophosphorous acid solution. Afterpurging 3 times with nitrogen by establishing a pressure of 4.10⁵ Pafollowed by decompression, the aqueous salt solution is concentratedfrom 50% by weight to 72.7% by weight in the course of 40 minutes, byevaporation, under a constant pressure of 9.10⁵ Pa, of some of the waterpresent in the mixture; the temperature then reaches 184.3° C.

Afterwards the following steps are carried out successively:

Step 1

The temperature of the 72.7% by weight aqueous salt solution is raisedto T1=209.2° C. in the course of 50 minutes while maintaining theautogenous pressure. A pressure of 1.65 MPa is then reached. The waterpresent in the reaction composition is then distilled under a pressureof between 1.65 and 1.45 MPa in the course of 2 hours, so as to obtain acomposition temperature of T2=282.7° C.;

Step 2

The autoclave is decompressed to atmospheric pressure in the course of 1hour 10 minutes and, at the same tee, the temperature of the compositionis raised to the value T3=306.2° C., while continuing to ensure regulardistillation of water; and

Step 3

The polycondensation reaction is completed operating under atmosphericpressure with a composition temperature raised to 315° C. for a periodof 45 minutes.

Stirring is stopped and a nitrogen pressure is then established in theautoclave and the polymer is withdrawn. The latter, which is extrudedfrom the autoclave in the form of a rod, is cooled by passing into abath of cold water and it is then granulated and dried.

3) Results:

The polymer obtained is homogenous and has the appearance of asemi-crystalline polymer. It has the following characteristics:

    ______________________________________                                        Molecular characteristics:                                                    ______________________________________                                        NH.sub.2 TG =  35 meq/kg;                                                     COOH TG =      84 meq/kg;                                                     MPP TG =       25 meq/kg;                                                     BHT content =  9.9 mM/kg, or 0.213% by                                                       weight;                                                        ______________________________________                                    

the calculated number-average molecular mass is 14,9 14 g/mol;

IV (m-cresol) =120 ml/g;

basicity losses in the distillates; 0.5886 amino equivalents, giving atotal basicity loss of 2.19%.

    ______________________________________                                        Thermal properties:                                                           ______________________________________                                        Tg =             135° C.;                                              Tcr =            251° C.                                               m.p. =           300° C.;                                              difference ΔT =                                                                          m.p. - Tcr is 49° C.                                  ______________________________________                                    

Thermomechanical values:

The polymer obtained is mixed with 4.5 mm long glass fibre 429 YZ fromOWENS CORNING, introduced as a molten Jet into a LEISTRITZ co-rotatingtwin-screw extruder-degasser containing screws having a diameter D of 34mm and a length of 35 D, and comprising: a feed zone, a heated mixingzone (comprising a degassing well) and a die. The glass fibre contentrepresents 40% by weight of the total polymer+glass fibres. The mainoperating parameters of the extruder-degasser are as follows:

    ______________________________________                                        temperature of the mixing zone                                                                        310° C.,                                       temperature of the die  300° C.,                                       devolatilisation pressure                                                                             200.10.sup.2 Pa,                                      speed of rotation of the screw                                                                        150 revs/min,                                         flow rate of the material                                                                             9 kg/hour,                                            residence time          2 minutes.                                            ______________________________________                                    

The filled polymer, which is collected at the extruder outlet in theform of a rod, is cooled rapidly in a water bath at 20° C. and is thencut into granules, which are packed in a sealed bag to prevent anymoisture being taken up again before injection moulding.

The injection-moulded test pieces have a bending temperature under load(BTUL) of 261° C. under 1.8 MPa in accordance with the standard NFT51005.

With regard to the moulding of the test pieces, this is carried out on aBATTEN[ELD machine under the following conditions:

    ______________________________________                                        temperature of the material                                                                      315° C.,                                            temperature of the mould                                                                         140° C. (injection termed                                              cold mould injection),                                     injection pressure 100 MPa,                                                   holding pressure   35 MPa,                                                    cooling time       25 seconds,                                                cycle time         50 seconds,                                                injection flow rate                                                                              7.5 cm.sup.3 /second.                                      ______________________________________                                    

Comparative Example

In this comparative example it is shown that in the absence ofhexamethylenediamine in the starting composition the homopolymer basedon terephthalic acid and 2-methylpentamethylenediamine which issynthesised has, when it is loaded with 40% by weight of glass fibre andwhen it is injected in a cold mould, a BTUL which is well below 240° C.

The semi-crystalline homopolyamide derived from terephthalic acid and2-methylpentamethylenediamine is prepared by a process in the moltenmass, of the type described in Example 1 above:

1) Preparation of the terephthalic acid/2-methylpentamethylenediaminesalt in aqueous solution:

The reaction is carried out in a 500 liter reactor equipped with:

a heating system,

a system permitting sweeping with nitrogen and maintenance of anoxygen-free atmosphere, and

a helical stirrer.

The following are introduced cold into the reactor:

49,446 kg of terephthalic acid (297.87 mole),

35.935 kg of 2-methylpentamethylenediamine (309.79 mole), and

128.07 kg of water.

The temperature of the composition is raised to 60° C. and the mixtureis stirred for 2 hours, maintaining sweeping with nitrogen. The pH thenreaches a value of 9.21; in this example a 4% molar excess of2-methylpentamethylenediamine is used.

Part of the water present in the mixture is then evaporated. Theequipment used comprises a 400 liter non-stirred stainless steelautoclave equipped to operate at up to 130° C. and at a pressure of 0.8MPa. It is provided with:

a heating system,

a system enabling it to be placed under nitrogen, and

a circuit permitting condensation and collection of the volatileproducts.

All of the aqueous salt solution prepared above is transferred into thisautoclave. After purging 3 times with nitrogen by application of apressure of 4.10⁵ Pa followed by decompression, the aqueous saltsolution is concentrated from 40% to 69.2% by weight in the course of 30minutes, by evaporation, under atmospheric pressure, of some of thewater present in the mixture; the temperature then reaches 103° C.

2) Polycondensation in an autoclave:

The apparatus used comprises a 200 liter stirred stainless steelautoclave equipped to operate at up to 320° C. and at a pressure of 2.2MPa. It is provided with:

a double-walled heating system operating by a heat transfer fluid,

an anchor-type stirrer,

a system allowing the autoclave to be placed under nitrogen pressure,

a circuit enabling the volatile products to be condensed and collected,

and a device for establishing a pressure lower than atmosphericpressure.

All of the aqueous solution concentrated to 69.2% by weight of salt istransferred to this autoclave. The procedure is then in accordance withthe same method as that indicated in Example 1, with the followingvariations:

In Step 1

The temperature of the aqueous 72.7% by weight salt solution is raisedto T1=180° C. in the course of 20 minutes, maintaining the autogenouspressure. A pressure of 0.85 MPa is then reached. The water present inthe reaction composition is then distilled under a constant pressure of0.85 MPa in the course of 2 hours 45 minutes so as to obtain acomposition temperature of T2=275° C.;

In Step 2

The autoclave is decompressed down to atmospheric pressure in the courseof 1 hour 10 minutes and, at the same time, the temperature is raised to298° C. while continuing to ensure regular distillation of water; and

In Step 3

The application of a reduced pressure of 533.10² Pa is then establishedin the course of 22 minutes, whilst at the same time raising thetemperature of the composition to 300° C., and the polycondensation iscompleted by continuing to stir the composition at 300° C. under 533.10²Pa for a further 20 minutes.

3) Results:

in respect of the molecular characteristics of the polymer:

NH₂ TG=68.8 meq/kg;

COOH TG=36.1 meq/kg;

MPP TG=15 meq/kg;

the calculated number-average molecular mass is 13899 g/mol;

IV (m-cresol)=105.1 ml/g;

basicity losses in distillates: 1.7177 amino equivalent, which gives atotal basicity loss of 2.39%;

with regard to the thermal properties:

Tg=143° C.;

Tcr=174° C.;

m.p.=285° C.;

the difference ΔT=m.p. - Tcr is 111° C.;

with regard to the thermomechanical characteristics of the polymerfilled with 40% by weight of glass fibres:

* Operating parameters of the extruder-degasser having been modifiedwith respect to the data in Example 1:

temperature in the mixing zone, 295° C.,

temperature of the die: 290° C.;

* Conditions for moulding test pieces having been modified with respectto the data in Example 1:

temperature of the material: 295° C.,

injection pressure: 80 MPa.

* BTUL=146° C.

EXAMPLE 2

In this example the preparation of a semi-crystalline copolyamide fromterephthalic acid, 2-methylpentamethylenediamine andhexamethylenediamine (60 mol % in the mixture of diamines) by thethermal polycondensation process conducted in solution termed the "thirdconvenient process" is described.

1) Preparation of the reagents

The reaction is carried out in a small 100 ml cylindrical glass reactorprovided with an anchor-type stirrer. The reactor is heated by immersingthe latter in a bath of Lipowitz alloy heated to above 180° C. Thereactor is also equipped with:

a system permitting sweeping with nitrogen,

a circuit per, hitting condensation and collection of the volatileproducts,

and a device for establishing a pressure lower than atmosphericpressure.

The following are introduced cold into the reactor:

13.75 g of dry and crystalline hexamethylenediamine/terephthalic acidsalt (0.04876 mol),

5.40 g of terephthalic acid (0.03253 mol),

3.96 g of 2-methylpentamethylenediamine (0.03414 mol), and

30 g of 1,3-dimethyl-2-imidazolidone.

The charges correspond to a 4.99% molar excess of2-methylpentamethylenediamine, which is a 1.98% molar excess of aminereagent.

2) Polycondensation:

The following steps are carried out successively:

Step 1''

Under a nitrogen atmosphere, the temperature is raised to 215° C. andthe water of amidification is removed by regular distillation underatmospheric pressure over a period of 30 minutes;

Step 2''

Under a nitrogen atmosphere the temperature of the reaction compositionis raised to 260° C. and the remainder of the water and the solvent areremoved by distillation under atmospheric pressure over a period of 45minutes;

Step 3''

The polycondensation reaction is completed by allowing the reactioncomposition, which has been heated to a temperature of 330° C., toreact, operating under a reduced pressure of 0.1.10² Pa for a period of15 minutes.

3) Results:

The polymer obtained is homogeneous and has a semi-crystallineappearance. It has the following characteristics:

Molecular characteristics:

VI (m-cresol)=82.3 ml/g;

basicity losses in the distillates:

9.48.10⁻³ amino equivalents, which gives a total basicity loss of 5.72%.

thermal properties:

Tg=140° C.;

Tcr=296° C.;

m.p.=320° C.;

the difference ΔT=m.p. - Tcr is 24° C.

EXAMPLE 3

In this example the preparation of a semicrystalline copolyamide fromterephthalic acid, 2-methylpentamethylenediamine andhexamethylenediamine (70 mol % in the mixture of diamines) by the massprocess termed the "second convenient process" is described.

1) Preparation of the diamines (2-methylpentamethylenediamine andhexamethylenediamine)/terephthalic acid salt in aqueous solution:

The reaction is carried out in a 2 liter glass reactor equipped with:

a heating system,

an anchor-type stirrer,

a system allowing sweeping with nitrogen and maintenance of anoxygen-free atmosphere, and

a system permitting condensation of the volatile products.

The following are introduced cold into the reactor, which is swept witha gentle stream of nitrogen:

350 g of hexamethylenediamine/terephthalic acid salt (1.2411 mols),

88.3 g of terephthalic acid (0.5319 mol),

66.7 g of 2-methylpentamethylenediamine (0.5750 mol) and

500 g of water.

A pH of 9.20 is obtained; in this example an 8.1% molar excess of2-methylpentamethylenediamine is used, which is a 2.43% molar excess ofamine reagent.

2) Polycondensation in an autoclave:

The equipment used consists of a stirred 1 liter stainless steelautoclave equipped to operate at up to 340° C. and a pressure of 3 MPa.It is provided with:

a double-walled heating system operating by a heat transfer fluid,

a frame-type stirrer,

a system allowing the autoclave to be placed under nitrogen pressure,

a circuit enabling the volatile products to be condensed and collected,

and a device for establishing a pressure lower than atmosphericpressure.

820 g of the aqueous salt solution prepared above are introduced with0.35 g of a 50% by weight aqueous hypophosphorous acid solution.

The procedure is exactly as indicated above in Example 1 up to the endof Step 1, with only the following variations:

the aqueous salt solution is concentrated from 49.75% by weight to 69.3%by weight; the temperature then reaches 194° C.;

in Step 1 the temperature at the start of distillation is 229° C., theheating period then being 20 minutes and an autogenous pressure of 1.8MPa is reached. The water present in the reaction composition is thendistilled under this pressure in the course of 1 hour 35 minutes and thetemperature T2 reached at the end of this period is 224° C.

Afterwards, the following steps are carried out successively:

Step 2':

The reactor is emptied rapidly in the course of 10 minutes; during thisperiod the water vapour pressure is lowered from the autogenous pressureto the atmospheric pressure value. The polymer formed, which is aprepolymer, is recovered and it is then cooled and converted to finepowder by grinding.

The prepolymer obtained has a semicrystalline appearance. It has thefollowing molecular characteristics:

    ______________________________________                                               NH.sub.2 TG =                                                                           122.5 meq/kg;                                                       COOH TG = 123 meq/kg;                                                         MPP TG =  5 meq/kg;                                                    ______________________________________                                    

BHT content=2.7 mM/kg, or 0.058% by weight;

the calculated number-average molecular mass is 8071 g/mol;

VI (H₂ SO₄)=14.2 ml/g;

basicity losses in the distillates: 0.1235 amino equivalent, which givesa total basicity loss of 3.41%.

Step 3':

The reaction for completion of the polycondensation is effected bycarrying out the postcondensation in the solid phase of the prepolymerin powder form obtained.

The reaction is carried out in a small 100 ml cylindrical glass reactorprovided with an anchor-type stirrer. The reactor is heated by immersingthe latter in a bath of Lipowitz alloy heated to above 180° C. Thereactor is also equipped with:

a system allowing sweeping with nitrogen,

and a device for applying a pressure below atmospheric pressure.

25 g of prepolymer powder are introduced cold into the reactor and thereactor is then swept with nitrogen in order to remove all traces ofoxygen and finally the temperature is raised to 260° C. under a reducedpressure of 0.66.10² Pa for a period of 2 hours 30 minutes.

3) Result:

The polymer obtained has a semi-crystalline appearance. It has thefollowing characteristics:

molecular characteristics:

VI (H₂ SO₄)=148 ml/g;

thermal properties:

Tg=127° C.;

Tcr=310° C.;

m.p.=322° C. and 344° C.;

the difference ΔT=m.p. - Tcr has values of 12° C. and 34° C.

We claim:
 1. Semi-crystalline, semi-aromatic copolyamide obtained fromterephthalic acid or a derivative and 2-methylpentamethylenediamine,which copolyamide has a glass transition temperature Tg of at least 120°C. and a bending temperature under load under 1.8 megapascal of at least240° C. when the copolyamide is filled with at least 10 to 60% of apadding or reinforcing filler of fibrous nature and then molded, aviscosity index of at least 60 ml/g and a number average molecularweight of at least 9000 g/mol, the said copolyamide having recurringunits of formula (I) , (II) , (III), (IV), and (V): ##STR3## (V)denoting the structure derived from bis-hexamethylenetriamine; themolecular ratio of units (I) with respect to the sum of the units(II)+(III)+(IV) is 1;the amount of units (III) in the mixture (II)+(III)is in the range ranging from 0 to 5 mol % and that of the units (II),with respect to the same reference, is in the range ranging from 100 to95 mol %; the amount of units (IV) in the mixture (II)+(III)+(IV) is inthe range ranging from 40 to 90 mol %; and also having a proportion ofthe units (V) derived from bis-hexamethylenetriamine, expressed as apercentage by weight of bis-hexamethylenetriamine with respect to theweight of the copolyamide obtained, which is less than 0.5%. 2.Copolyamide according to claim 1, having a structure in which the amountof units (IV) in the mixture (II)+(III)+(IV) is within the range rangingfrom 45 to 75 mol %.
 3. Shaped article selected from the groupconsisting of a molded article, a filament, and a film, obtained fromthe colpolyamide according to any one of the above claims 1 to
 2. 4.Semi-crystalline, semi-aromatic copolyamide obtained from terephthalicacid or a derivative and 2-methylpentamethylenediamine, whichcopolyamide has a glass transition temperature T_(g) of at least 120° C.and a bending temperature under load under 1.8 megapascal of at least240° C. when the copolyamide is filled with at least 10 to 60% of apadding or reinforcing filler of fibrous nature and then molded, aviscosity index of at least 60 ml/g and a number average molecularweight of at least 9000 g/mol, the said copolyamide having recurringunits of formula (I), (II), (III) and (IV): ##STR4## (IV) denoting thestructure derived from bis-hexamethylenetriamine; the molecular ratio ofunits (I) with respect to the sum of the units (II)+(III) is 1;theamount of units (III) in the mixture (II)+(III) is in the range from 40to 90 mol %; and also having a proportion of the units (IV) derived frombis-hexamethylenetriamine, expressed as a percentage by weight ofbis-hexamethylenetriamine with respect to the weight of the copolyamideobtained, which is less than 0.5%.
 5. A copolyamide according to claim1, having a structure in which the amount of units (III) in the mixture(II)+(III) is in the range ranging from 45 to 75 mol %.
 6. A shapedarticle according to any one of the above claims 4 or 5.